1. Field of the Invention
The present invention is generally related to polymers with benzoxazine groups in their main chains, and more particularly to polymers prepared through the Diels-Alder reaction with benzoxazine groups in their main chains.
2. Description of the Prior Art
Similar to other thermosets, polybenzoxazines are conventionally obtained from the thermally curing reactions of small molecular, mono-or difunctional benzoxazine compounds. Most of the benzoxazine monomers are powder, which are hard to be processed into films.
Polymers possessing benzoxazine groups in the main chains could be obtained using difunctional amine and phenol derivatives as monomers. However, the number-average-molecular weights of the polybenzoxazines are not high (around 1000 to 4500 g/mol).
One example reported by Ishida and coworkers is benzoxazine-containing polyesters by using a benzoxazine-containing diol as amonomer. The molecular weights of the obtained polymers are as high as 30,000 g/mol. However, the thermal stability of the cured polybenzoxazines is not comparable with the conventional crosslinked benzoxazine resins. (Kiskan, B.; Yagci, Y.; Ishida, H. J Polym Sci Part A: Polym Chem 2008, 46, 414. )
In light of the above-mentioned problems, a new polybenzoxazine is still in great demand to fulfill the requirements of good thermal stability, and high mechanical strength. This remains an important research aspect in the industrial practical applications.